1. Field of the Invention
The present invention relates generally to a method and system of recovering gold from alluvial placer deposits.
2. Description of Related Art
Placer gold mining historically relied upon a sluice box, and its variants, to separate the gold from the gravel matrix. The sluice has been the primary method of gold recovery from its historical introduction to the present.
A typical alluvial mining plant uses a very large volume of water to transport the larger size gravels over the recovery sluice. Depending on volume being processed, water usage can be over 5000 gallons per minute. The percentage recovery of gold in a typical sluice box is 20% to 40% of all gold run through it. This low recovery percentage is even be lower when the gold is still attached to the host rock, such as in matrix pieces. Matrix pieces usually comprise quartz with a small percentage of gold, are lower in specific gravity than pure gold nuggets and are thus commonly washed out of a sluice recovery system. Because there has been no efficient way to recover this percentage of gold in the past, the lost revenue to the operator is significant. Many placer companies find it difficult to financially survive, even in rich areas, when their recovery is so low.
The process of a sluice recovery system is not environmentally friendly. The large volume of water required creates obstacles in sourcing and cleaning the water of solids before returning to the source. This typically involves using large settling ponds, which implicates corresponding costs of land use, construction costs, excess fuel burning during construction and final reclamation. In addition, the pumping and dewatering of such large volumes of water requires significant power.